A wireless transmit/receive unit (WTRU) and a network perform transmit power control in order to adjust the transmit power level in an optimal level. Both an inner loop power control and an outer loop power control are performed for closed loop transmit power control. The inner loop power control generates a transmit power control (TPC) command based on a signal-to-interference ratio (SIR) measurement and an SIR target. The outer loop power control adjusts the SIR target based on block error rate (BLER) measurements.
The third generation partnership project (3GPP) has introduced high speed downlink packet access (HSDPA). In HSDPA, every user is allocated a dedicated physical channel (DPCH) in both uplink and downlink directions to exchange higher layer signaling information between a WTRU and a network. As there can be a large number of users in a cell, this might lead to a waste of the channelization codes in the downlink. In order to save such channelization codes, a fractional dedicated physical channel (F-DPCH) has been introduced.
An F-DPCH is a special downlink channel carrying only TPC commands generated at layer 1. Several HSDPA users share the same F-DPCH channelization code, and TPC commands for several users are time-multiplexed onto one F-DPCH channelization code. However, the F-DPCH does not carry any transport channels. Therefore, the outer loop power control cannot adjust the SIR target based on the transport block BLER on the F-DPCH.